Solenoid apparatus for ultra-high vacuum environments

ABSTRACT

ELECTRIC SOLENOID APPARATUS DESIGNED FOR USE IN AN ULTRAHIGH VACUUM ENVIRONMENT, CHARACTERIZED IN THAT THE SOLENOID COIL IS CONTAINED IN A TIGHTLY SEALED ANNULAR CHAMBER, ELECTRICAL POWER BEING SUPPLIED TO THE COIL VIA TERMINALS EXTENDING THROUGH AN END WALL OF THE CHAMBER TO ACTUATE A SOLENOID PLUNGER EXTERNAL OF THE CHAMBER. IN ACCORDANCE WITH AN IMPORTANT FEATURE OF THE INVENTION, THE COIL HOUSING CONSISTS OF A PLURALITY OF SEPARABLE SECTIONS BETWEEN WHICH SEAL ELEMENTS ARE ARRANGED, SPRING MEANS EXTERNAL OF THE SEALED CHAMBER BEING PROVIDED TO BIAS THE HOUSING SECTIONS TOGETHER TO TIGHTLY COMPRESS THE SEAL ELEMENTS. CONSEQUENTLY, THE COIL MAY BE WOUND UPON A CYLINDRICAL NON-MAGNETIC INSULATING CORE THAT DEFINES THE INNER WALL OF THE COIL HOUSING, THEREBY FORMING AN INTERCHANGEABLE COIL AND CORE UNIT. THE OUTER WALL IS FORMED OF A MAGNETIC MATERIAL AND DEFINES A PART OF THE RETURN FLUX PATH FOR THE SOLENOID COIL.

Feb. 16, 1971 ANASTASIQ ETAL 3,564,469 SOLENOID APPARATUS FOR ULTRA-HIGH VACUUM ENVIRONMENTS Filed July 22, 1969 mvau'rons Thamas A. Anas/as/o Richard G Poke/ski United States Patent 3,564,469 SOLENOID APPARATUS FOR ULTRA-HIGH VACUUM ENVIRONMENTS Thomas A. Anastasio, Glen Burnie, and Richard G.

Pokorski, Highland, Md., assignors to Dividean Incorporated, Severn, Md., a corporation of Maryland Filed July 22, 1969, Ser.'No. 843,403 Int. Cl. H01f 7/08 US. Cl. 335-260 17 Claims ABSTRACT OF THE DISCLOSURE Electric solenoid apparatus designed for use in an ultrahigh vacuum environment, characterized in that the solenoid coil is contained in a tightly sealed annular chamber, electrical power being supplied to the coil via terminals extending through an end wall of the chamber to actuate a solenoid plunger external of the chamber. In

Various solenoid constructions of the type including separable housing sections have been proposed in the prior art, as evidenced, for example, by the patents to Viale No. 3,181,040, Kumm No. 3,252,482 and Pratt No. 2,852,637. In the Kumm patent, gasket means are provided between the separable sections, and in Viale et al., snap ring means are provided for securing together the separable sections to form a rigid housing. The use of such known electromagnetic solenoid constructions in high (and ultra high vacuum systems, however presents several ditficult problems, such as deterioration of the solenoid coil as a consequence of evaporation of coil insulation, deterioration of the moving parts due to seizing or galling between clean unoxidized surfaces, and deterioration of the vacuum because of outgassing of the coils and other parts.

One proposed solution to the problem of designing an improved solenoid construction for use in high and ultrahigh vacuum environments (i.e., in the vacuum range of to 10 torr) is to encapsulate the solenoid coil in a vacuum tight housing, so that the coil itself need not be vacuum worthy (since it will be outside the vacuum environment), but rather can be designed primarily in view of electrical, mechanical and thermal considerations. The housing must be such that it provides a tubular section extending through the center of the coil and within which a ferromagnetic plunger is displaceable under the influence of the magnetic field produced upon energization of the coil.

Accordingly, the primary object of the present invention is to provide an electromagnetic solenoid apparatus including a sectional housing containing a chamber in which is mounted the solenoid coil, characterized in that improved seal means are provided between the housing sections to tightly seal the coil chamber. In accordance with an important constructional feature of the invention, the seal means include spring means external of the coil chamber for biasing together the housing sections to tightly compress the seal elements, said spring means preferably being in the form of a disk spring.

3,564,469. Patented Feb. 16, 1971 A more specific object of the invention is to provide a solenoid apparatus of the type described above in which the housing chamber is annular and includes a separable inner Wall portion formed of an insulating non-magnetic material such as a high alumina ceramic material. Consequently, the non-magnetic section constitutes a replaceable coil supporting core upon which the solenoid coil is wound. In order to inspect or replace the solenoid coil, the housing may be readily disassembled for replacement or repair of the core and coil unit.

In accordance with another object of the invention, the coil chamber is filled with a leak detectable gas, such as helium having a pressure of about 15 pounds per square inch, which gas serves not only as an indicating means for detecting leakage in the seal means, but also as a heat transfer medium for minimizing thermal shock to the coil to allow heat to be removed from the entire structure, by means of cooling coils or heat sinks in contact with the housing.

A further object of the invention is to provide a solenoid aparatus in which the outer housing section is formed of a magnetic material to provide a return path for the magnetic flux, a removable magnetic armature stop being provided with the housing for limiting the extent of movement of the plunger and for assisting in shaping the force-stroke characteristic of the solenoid apparatus.

In accordance with a more specific object of the invention, the disk spring that biases the housing components together to compress the seal elements is supported adjacent its outer peripheral edge portion by releasable clamp means, which in the preferred embodiment, are axially shiftable to a released position relative to the housing, said clamp means being normally biased by the disk spring in the opposite direction toward a locked position relative to the housing. In order to permit this movement of the clamp means, the face of the housing end plate section is chamfered adjacent the outer periphery of the disk spring, thus permitting the disk spring to be overflexed by releasing tool means operable by means of a strong vise or the like.

Other objects and advantages of the invention will become apparent from a study of the following specification, when viewed in the light of the accompanying drawing, in which:

FIG. 1 is an end view of the assembled solenoid apparatus;

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1 the apparatus being shown in the energized condition; and

FIG. 3 is a partially sectioned view illustrating the manner in which the spring is overflexed during assembly and disassembly of the apparatus.

Referring now to the drawing, the solenoid apparatus includes a housing 2 having a cylindrical outer section 4 formed of a magnetic material (for example, 410 stainless steel) and containing at one end a bore, said outer section having at its other end an end wall 4a containing a plunger opening 6. The housing includes also a separable cylindrical inner section 8 that cooperates with the outer section to define an annular chamber 10 in which is arranged the annular solenoid coil 12. The separable inner housing section 8, which forms a coil supporting core upon which the turns of coil 12 are wound, is formed of a non-magnetic electrically insulating material (for example, a high alumina ceramic material). The core section includes intermediate its ends a pair of integral axiallyspaced flanges 8a, 8b that support the ends of solenoid coil 12.

The open end of housing 2 is adapted to be closed by an annular end plate 14 also formed of stainless steel and containing a central opening 16 in which is mounted a plunger stop element 18. The stop element is provided at one end with a flange portion 18a that is locked within a corresponding counterbore recess contained in the end plate 14 by a split resilient retaining ring 20'. As shown in FIG. 2, the other end of the stop element terminates within the inner housing section 8 and limits the left-hand extent of travel of the ferromagnetic solenoid plunger 22. The

end plate 14 contains a pair of diametrically-arranged through bores in which are mounted a pair of conductive lead-in terminals 24 and 26, respectively, for supplying electrical energy to the ends of the solenoid coil 12. More particularly, terminal 24 is connected with one winding =end'via conductive contact spring 27 and conductor 28 that extends through a corresponding opening contained adjacent the central portion of flange 8a, while the other 'terminal 26 is connected with the other winding end via conductive contact spring 29 and conductor 30 that extends through a corresponding slot contained in the outer to the end plate with low vapor pressure BT brazing material.

In accordance with the present invention, improved seal means are provided, between the separable housing sections and the end plate for sealing the coil chamber 10. More particularly, first and second annular seals 38 and 40 are provided between the end plate 14 and the adjacent ends of the outer and inner housing sections 4 and 8 respectively, and a third annular seal 42 is provided be- :tween the other extremity of the inner core section 8 and the end wall portion 4a of'the outer housing section 4.

Each of the annular seals is formed of a material having high compressibility, such as a soft metal for example, gold) or an elastomeric seal such as Vitron rubber of Teflon). In order to compress the seals and thereby seal the coil chamber 10, annular disk spring 46 is provided the outer peripheral portion of which is connected with the housing by clamp means 48, the central portion of the spring serving to bias end plate 14 and inner core section 8 to the right relative to housing section 4. The disk spring contains oversize openings that receive the free extremities of terminals 24 and 26, whereby free electrical lead-in access is afforded to the solenoid coil.

The clamping means. 48 comprises a pair of sections 48a, 48b each having at one end a flange portion 480 adapted to support the outer peripheral portion of the disk spring, and at the other end a reversely chamfered flange portion 48d adapted to extend in locked engagement with a correspondingly chamfered lock shoulder 4b on the housing section 4. It will be apparent that the disk spring normally biases the clamp means 48 to the left relative to housing section 4 toward the locked position illustrated in FIG. 2.

Accordingly an important feature of the invention, the solenoid apparatus may be readily disassembled to afford replacement of the solenoid coil and core unit. As shown in FIG. 2, the free end surface 14a of end plate 14 is chamfered to define a generally conical configuration, thereby to permit overflexing of the outer periphery of the disk spring 46 by the axially biased releasing tool 50 as shown in FIG. 3. Thus when the outer peripheral portion of the spring disk is flexed to the right against the chamfered end surface 14a as shown in FIG. 3, the clamp means may be displaced to the right to free the chamfered flange 48d from the lock shoulder 4b, and upon removal of the clamp sections 48a and 48b, the end plate 14, inner core section 8, and solenoid coil 12 may be removed from the outer housing section 4. Owing to the provision of the contact springs 27, 29, there is no need to directly connect the coil wires to the terminals, thereby eliminating the need for excess wire from the coil to the terminals. Furthermore, coil replacement is simplified since there is no permanent connection of wire leads to the terminals.

Following inspection, repair or replacement of the coil and core unit, is is inserted into the outer housing section, and the end plate is positioned to close the chamber 10, whereupon force is applied to the spring 46 by tool 50 (for example, by a heavy duty vise) to cause overflexure of the outer periphery of the spring against the chamfered surface 14a, whereupon the clamping sections 48a and 48b are returned to the position shown in FIG. 3. Upon gradual release of the biasing force on tool 50', the spring 46 returns to its normal configuration biasing clamp means 48 to the left to the locked (FIG. 2) position relative to the housing section 4, while simultaneously biasing the end plate 14 and core 8 to the right to maintain compressive force on the annular seals 38, 40- and 42 to seal the annular chamber 10 in which the solenoid coil 12 is contained.

The solenoid apparatus may be utilized in various desired applications in a high vacuum environment. For example, as shown in FIG. 2, the housing 4 may be bolted to a support 56 containing an opening through which the plunger 22 extends. Spring means 58 normally bias plunger 22 to the right, whereby upon energization of the solenoid coil 12 via terminals 24, 26 and leads 28, 30, plunger 22 is attracted to the left against stop 18 as shown in FIG. 2. Upon de-energization of the solenoid coil, plunger 22 is shifted to the right by spring 58.

The annular disk spring 46 has a high modulus of elasticity (i.e., is highly resistant to distortion) and is formed of a strong material (for example, high chromium steel). Since the core 8 is preferably formed of a non-magnetic material such as a high alumina ceramic, it has unity permeability and will not gall or seize with metals. As the housing expands or contracts upon change in temperature, the disk spring 46 flexes to maintain the compressive pressure on seal rings 38, 40 and 42, whereby a tight seal is maintained even when the housing dimensions vary in response to temperature fluctuation.

Since the plunger is not an integral part of the unit, a variety of plungers may be utilized with the solenoid housing. The plunger stop 18 may be removed upon release of the retaining ring 20 to permit insertion of the plunger from either end of the housing, thereby affording push, pull or push-pull solenoid operation. In accordance with another important feature of the invention, the stop is formed of a magnetic material to permit shaping of the force-stroke characteristic of the solenoid apparatus. Thus, various shapes of plungers and plunger stops will provide various force-stroke curves as desired. Owing to the low eddy-current-loss alumina core the solenoid apparatus is operable on either alternatingcurrent or directcurrent power. In the case of alternating-current operation, a shading coil (not shown) may be provided on the armature stop to avoid chatter.

In accordance with another important feature of the invention, during assembly the housing is evacuated and back-filled with helium gas having a pressure of about 15 pounds per square inch, which gas permits easy leak detection by means of a helium mass spectrometer leak detector. Moreover, the helium charge in the coil chamber allows a greater duty cycle, because heat is transferred from the coil to the housing more readily due to the higher thermal conductivity of helium as compared to air. The solenoid coil is preferably designed for resistance to nuclear radiation.

The non-welded design of the apparatus is free of virtual leaks, and typical ultra-high vacuum applications of the apparatus include shutter actuation, crystal cleaving, mask changing and electromechanical latching.

What is claimed is:

1. Electromagnetic solenoid means adapted for use in an ultra high vacuum environment, comprising:

a housing open at one end and containing a chamber;

a solenoid coil arranged in said housing chamber;

means including an end plate for closing the open end of said housing;

and seal means affording a seal between said end plate and said housing, comprising at least one seal element arranged between said end plate and said housing, and spring means arranged externally of said chamber for biasing said end plate in the axial direction toward said housing to tightly compress said seal element.

2. Apparatus as defined in claim 1, wherein said housing, said chamber and said coil are each of an annular configuration.

3. Apparatus as defined in claim 2, wherein said spring means comprises a generally circular disk spring.

4. Apparatus as defined in claim 3, and further including means removably connecting the outer peripheral edge portion of said disk spring with said housing, the central portion of said disk spring being in biasing engagement with said end plate.

5. Apparatus as defined in claim 4, wherein said spring connecting means comprises split collar clamp means.

6. Apparatus as defined in claim 5, wherein said clamp means is displaceable between locked and released positions relative to said housing, said spring means being arranged to bias said clamp means toward the locked position.

7. Apparatus as defined in claim 6, wherein the exterior surface of said end plate is chamfered to permit axial movement of said clamp means and the adjacent outer peripheral edge portion of said disk spring toward said released position.

8. Apparatus as defined in claim 2 wherein said one seal element comprises an outer annular seal element arranged between the outer annular wall portion of said housing and said end plate.

9. Apparatus as defined in claim 8, wherein said seal means includes also an inner annular seal element arranged between the inner annular wall portion of said housing and said end plate.

10. Apparatus as defined in claim 9, wherein the housing consists of at least two separable sections one of which is annular and defines the annular inner wall portion of said housing, said one section being formed of non-mag netic insulating material and defining a spool upon which the turns of said solenoid coil are wound, the other of said housing sections being formed of a magnetic material.

11. Apparatus as defined in claim 10, and further including at the end of the housing remote from said open housing end a third seal element arranged between said one housing section and said other housing section, each of said seal elements being formed of soft metal wire.

12. Apparatus as defined in claim 2, and further including electrical lead-in means extending through said end plate for energizing said solenoid coil.

13. Apparatus as defined in claim 12, wherein said lead-in means comprises at least one terminal member mounted in and extending through a corresponding bore contained in said end plate, and spring contact means electrically connecting said terminal member with said coil.

14. Apparatus as defined in claim 13, wherein said disk spring contains an opening affording access to said terminal member.

15. Apparatus as defined in claim 2, wherein said disk spring is annular, and further wherein said end plate contains a centrally-arranged opening, and an annular armature stop member removably mounted in said opening for limiting the axial movement of an armature member operable by said coil.

16. Apparatus as defined in claim 15, wherein said armature stop member is formed of a magnetic material for cooperating with said other housing section to shape the force-stroke characteristic of the apparatus.

17. Apparatus as defined in claim 1, and further including a charge of leak-detectable gas contained in said chamber.

References Cited UNITED STATES PATENTS 3,307,129 2/1967 Mangiafico 335-260X 3,327,264 6/ 1967 Rodaway 335-251X 3,462,116 8/1969 Wright 335-278UX GEORGE HARRIS, Primary Examiner U.S. Cl. X.R. 335278 

